Sheet moisture drying machine control mechanism



March 3, 1953 A. E. BENNETT SHEET MOISTURE DRYING MACHINE CONTROL MEOHANISM 3 Sheets-Sheet l Filed Jan. 28. 1952 March 3, 1953 A, E. BENNETT 2,629,939

SHEET MOISTURE DRYING MACHINE CONTROL MECHANISM l Filed Jan. 28. 1952 3 Sheets-Sheet 2 INVENTOR:

HND/TEW E. BEN/v: T7'

caw M( M I 1L March 3, 1953 A. E.BENNETT 2,629,939

SHEET MOISTURE DRYING MACHINE CONTROL MECHANISM Filed Jan. 28. 1952 3 Sheets-Sheet 3 r I' I l y* l INVENTOR' t .62 J* BY CMMOM [MubNL Patented Mar. 3, 1953 NITED STATES PATENT OFFICE SHEET MGTSTURE DRYING MAGHTNE CONTROL MECHANISM Andrew E. Bennett, Hingham, Mass., assigner to Mason-Neilan Regulator Company,

Boston,

14 Claims. i

This invention relates to control mechanism for use in connection with drying machines commanly employed industries concerned with the manufacture of papery textiles, synthetic material and the like 1cor reducing the moisture content of such material to a predetermined value, and more particularly the invention relates to means which coact with the moisture control mechanism in manner hereinafter to be described to reduce the temperature or" the drying machine during an interval that no sheet material is passing therethrough as may be occasioned3 for example, by a bre-ah in the sheet matei-iai. When the material is again introduced to the machine, the mechanism also functions to return the drying temperature to such value as may be required to provide a predetermined sheet moisture content. By this means, when a sudden reduction in moisture load has occurred, overheating of the drying machine is prevented and the damage resulting therefrom to the sheet when again instrcduced to the machine is avoided.

Drying machines of the type referred to comprise a plurality of heating elements, usually in the iorzr. or rotating drums or rolls, commonly ranged in one or more main drying sections, over which the material passes from the so-called riet end to the dry end of the machine, it being understood that the material being dried by machines of this type may be in the form of solid shee's such as paper, felt, cloth or the like, or may ocnsist o sheets in the form of strands for example, are commonly termed the Warp in the manufacture of cloth. And the control mechanism to which this invention relates is adapted to govern the heat input to a drying roll er rolls in one or more main drying sections to reduce the moisture ccntent ci the sheet material passing through the machine to a predetermined value. More particularly this invention relates 'to that type o sheet drying control mechanism 'wherein one or more drying rolls associated with a main drying roil section are used to reiect or indicate changes in sheet moisture, to whic lchanges the mechanism embodying this invention responds and varies the heat input, as for eX- ample steam, to a main section of drying rolls as required. to maintain the desired moisture content in the sheet as it leaves the machine. ln controls of this type it is customary to suppli7 steam to the indicating roll or rolls independently of the steam supplied to the main drying roll section, and by responding to changes in the rate of condensation of lsteam 'in an indicating roll, koccasioned by changes in the moisture content of the sheet passing over the rollI the flow of steam to the main drying roll section is Varied for the purpose of retaining the desired sheet moisture content. And the mechanism herein shown and described functions together with control mechanism of the afore-mentioned type to decrease the heat input to the machine when a break in sheet material occurs and thereafter to control the said heat input at a suitable value so that either overheatirrT or underheating of the material is prevented and the damage resulting therefrom avoided when the material is again introduced to the machine, at which time the heat input is again raised to such value as is required to maintain a selected sheet moisture oontent.

A preferred form of control mechanism embodying this invention is herein shown and described, Wherein a constant steam input is maintained to an indicating roll and changes in the rate of steam condensation in the said roll are measured by changes in roll pressure or temperature, thereby reflecting changes in sheet moisture, such mechanism being generally similar to that shown and described in a copending application for United States Letters Patent iiled October l0, 1951 under Serial No. 250,706, of which I am a ce-inventor. vand a modied form of control mechanism embodying this invention is also shown and described, wherein changes in the rate of steam condensation in the indicating roll are measured by changes in the rate of flow of steam to said roll.

It is an object of this invention to provide an improvement in control mechanism for maintaining the moisture of sheet material passing through a drying machine at a substantially constant value, including means for maintaining the temperature of the machine at a suitable value during a period when no material is passing therethrough, thereby preventing the sheet from becoming overheated or underheated and damaged when it is again passed through the machine.

t is an object of this invention to provide an improved control mechanism which responds to changes in moisture in a sheet of material passing over, one or more drying machine rolls having a separate steam supply from that which supplies the main drying section of the machine for the purpose of varying the heat input to the said main drying section and thereby maintaining a predetermined sheet moisture content, in combination with automatic means Which function with the aforesaid mechanism to reduce the heat input to the machine when a break in sheet material occurs to maintain the said heat input at a suitable value to prevent damage to the sheet material when again introduced to the machine, and thereafter to return the heat input to such value as may be required to provide a selected sheet moisture content.

It is an object of this invention to provide a rst means for governing the input of heat to a main drying section of a sheet moisture drying machine, a second means for measuring the rate of condensation of steam supplied to a sheet moisture indicating section of said machine for ./arying the value of the heat input governed by said nrst means, and a third means functioning with said second means to reduce the said heat input to a predetermined value when a break in sheet material occurs and the material is off the machine, to prevent overdrying or underdrying oi the material when again introduced thereto, and thereafter to increase the heat input to such value as may be required to again maintain a selected sheet moisture content.

While there is herein shown and described a preferred form of control mechanism wherein a controller which governs the steam input to a main drying roll section of a sheet material drying machine is responsive to roll pressure, it will be understood by those skilled in the art that the said heat input may also be governed by a controller responsive to roll temperature in said section or to the rate of flow of steam to the rolls of said section; and it will be further understood that while there is herein shown and described a preferred form of control mechanism including means responsive to changes in steam pressure in a sample roll having an independent constant steam input for the purpose of indicating changes in moisture in sheet material passing over the roll, as indicated in modified views such means may be responsive to roll temperature if desired, since changes in sheet moisture are redected by both pressure and temperature. And it will be again understood that while in one embodiment of this invention there is shown and described a simple form of means for switching the control from on-moisture load to ofi-moisture load, various well-known means may be employed without departing from the spirit of this invention. Further objects and advantages of the invention will be apparent from the following description when taken in connection with the accompanying drawings in which- Fig. i is a diagrammatic view, partly in perspective, of a control mechanism embodying this invention as applied to a paper drying machine;

Fig. 2 shows, in perspective, a modied construction of part of the mechanism shown in Fig. l;

Fig. 3 shows, in end elevation and enlarged, a modied construction of the mechanism shown in Fig. 2;

Fig. i is an enlarged View, in section, of a portion of the mechanism, the parts being in the reverse position from that shown in Fig. 1; and

Fig. 5 is a diagrammatic view of a modification or" the construction shown in Fig. 1.

Having reference to the drawings and particularly to Fig. 1, there is illustrated a portion of a drying roll section, generally indicated at 5, of a paper drying machine. The section 9 includes a plurality of rolls I which are connected in the usual manner by pipes II with a main steam header I2, supplied from a source not shown, by-

a conduit I3, and are also connected by means or condensate pickup pipes, not illustrated, and pipes I4 with a condensate conduit I5 leading to a separator, also not shown. The drying rolls i5 are rotated in unison by means not illustrated, and are engaged by a paper sheet I5 which passes over and under the rolls in the direction indicated by the arrow from the wet end to the dry end of the machine all as shown, the usual felt being omitted to simplify this description.

While there is herein illustrated a plurality of drying rolls I0 forming part of a drying roll section, it will be understood by those skilled in the are that the drying roll section may consist of one large roll, such as that employed in a Yankee Drier commonly used for drying light tissue, or may comprise any. other form of drying means suitable to the particular type of sheet material being processed.

Means for governing the iiow of steam to the rolls I0 to provide the temperature required to reduce the sheet moisture content to a predetermined value as the sheet leaves the machine is herein illustrated as a pressure controller, generally indicated at 20, which functions in connection with a motor valve 2| to vary the ow of steam through the supply conduit I3 as required to provide a selected sheet moisture content. The controller may be of any wellknown construction and for the purpose of this description, is shown diagrammatically in simpliiied form. It includes a spiral Bourdon coil 22, a control couple consisting of a nozzle 23 and dapper 24, a pneumatic proportioning device 25 and a pneumatic control point reset device 225. While the controller is shown without a booster pilot for speeding up the motor valve action and without a reset bellows or its equivalent for eliminating so-called drift, it will be understood that either or both of these devices may be employed if desired.

The Bourdon coil 22 is mounted with one end secured to a circular back plate 2l which in turn is rotatably mounted on the controller back plate indicated at 211. The spiral coil is provided With a central shaft 28 journalled in the plate 2l' at its inner end and at its outer end in an arm 29 which extends radially over the coil and is rigidly attached to the said plate 21. A motion transmitting arm 30 is secured to the shaft 28 which in turn is in operative connection with the free end of the coil. The fixed end SI of the coil communicates with a exible tube 32 which, as herein shown, connects with the header I2, the parts being arranged so that on an increase of pressure in the header, the coil unwinds turning the arm 30 clockwise, and on a decrease in header pressure, the opposite occurs.

The proportioning device 25 actuates one end of the dapper 24 which coacts with the nozzle 23 to vary the operating pressure in the system. Air or an equivalent uid, preferably under regulated pressure, is supplied to the nozzle 23, from a source not shown, through pipes 33 and 34, the former having a restriction 35 of less capacity than that of the nozzle orifice so that the nozzle pressure is governed by the relative position of the flapper in respect to the nozzle. The proportioning device 25 includes a bellows having a xed mounting 31 to which one end of the bellows is connected, the interior of the bellows being in communication with pipes 33 and 3f'. by means of a pipe 38. Secured to the free end 33 of the bellows is a post 40 which is also attached to a disc 4I, an expansion spring 42 being conned between the disc and a iixed member 43 so that the end of the flapper 24, which is pivotally connected to the post at 44, assumes a position which is proportional to the ilud pressure in the bellows 36, the overall bellows movement being determined by the rate selected for the spring 42. The other end of the :dapper 24 is engaged at 45 by one end of a lever 46 pivotally at 461 on a post 41 forming part of the control point reset device 26 to be described. The other end of the lever 46 is engaged by the free end of the coil arm 30 and the parts are so arranged that an increase in uid pressure in the steam header I2 causes the coil to unwind and turn the arm 30 clockwise, thereby moving the flapper 24 away from the nozzle 23. This movement results in a decrease in pressure in the proportioning bellows 36 causing the bellows to contract and return the apper to a throttling relation with the nozzle at a lower pressure` which pressure is proportional to the increase in steam pressure in the header I2. On a decrease in pressure in the header I2, the opposite occurs.

The motor valve 2|, of the 4iiuid pressure operated type and of any usual construction, is mounted in the steam conduit I3 by which the header I2 is supplied. As herein shown the valve 2I is of the reverse acting type. It has a valve member 49 connected with a stem 5i! which is actuated by a diaphragm 5I denning one wall of a uid pressure operating chamber 52, the pressure in which is opposed by a spring 53. The diaphragm chamber 52 is connected with the controller piping 33 and 34 by means of a pipe 341, the valve parts being arranged so that the valve ymember 49 moves toward closed position on a decrease in operating pressure. Thus when the pressure in the steam header I2 increases or decreases, the pressure in the nozzle 23 decreases or increases respectively in proportion thereto, thereby providing a proportional throttling action to the valve, and varying the flow of steam to the header I2 in a direction to return the pressure in the drying rolls I0 to a set value.

It will be understood by those skilled in the art that the pressure at which the controller is set depends on the initial position assumed by the apper in relation to the nozzle and that this in turn depends both on the radial position assurned by the coil arm 30 at a selected pressure in the header I2 and on the vertical position of the pivotal connection 61 between the lever 4S and post lll of the pneumatic reset device 26.

Suitable means for manually adjusting the radial position of the coil arm 39 is in the form of a hand Operated gear 54 `which meshes with a toothed section 55 on the plate 2i, the pipe 32 being provided with a flexible portion 56 to permit the coil to be rotated by the gear to any selected position within the range of control setting adjustment. When the coil is rotated counterclockwise the pressure setting is raised and vice versa. The manual control point setting device just described functions in connection with the pneumatic control point resetting device 26 in a manner to be hereinafter set forth.

Means for adjusting the initial sensitivity of the controller may be in the form of a rack i on which the nozzle 23 is mounted, movement toward the connection 45 between the flapper 24 and the lever 46 provides greater sensitivity and vice versa. To permit of this adjustment, the

,of the dapper in respect thereto. which a three-way valve 35 is mounted, serves 6. pipe 34 is provided with a flexible portion as indicated at 58.

The apparatus just described illustrates a simple form of -control mechanism for governing the valve 2| to maintain a set pressure in the header I2 and functions with apparatus to be described to vary the pressure setting and thereby the roll temperature as required to maintain the moisture content of the sheet as it leaves the machine at a selected value. And it will be understood that while there is sho-wn a pressure controller by way or illustration, a temperature or rate oi iiow controller may be equally well utilized, the object being to provide a roll temperature such as may be required for the purpose.

In the form of control apparatus shown in Fig. l means are provided for responding to minute changes in sheet moisture by maintaining a constant rate of steam input into a moisture indicating roll section, herein shown as a roll 5G, and responding to pressure or temperature in the said roll or to temperature changes at the roll surface. For this purpose, the roll 5d is provided with a separate steam supply through a conduit 6I from a source not shown, and with means for removing the condensate as by an internally mounted condensate pickup pipe, also not shown, which connects with a condensate discharge pipe having a steam trap 533 which in turn communicates with a discharge conduit 64. Steam flow through the supply conduit El is maintained at o. constant selected rate by means of a rate of ow controller', generally in dicated at which functions with a motor valve 68 for this purpose. The rate of ilow controller 65 may be of any suitable construction and herein shown comprises the usual mercury ma nometer 6l suitably filled with mercury @33 and having a connection @9 upstream o1 an orice 'Ill in the conduit 6l and a connection 'ii downstream of said orifice. A iioat i2, pivotally connected at "i3 to one end of a lever 'ifi having a pivotal mounting 'i5 in the :nanometer casing, serves to rotate the lever about the pivotal mounting on a basis which is substantially proportional to changes in the pressure diierential across the oriii-ce lll and therefore to changes in the rate of steam flow. The other end of the lever le has a pivotal connection with a iapper operating arm 16, a locking member being provided for clamping the arm in any rotary position desired. The free end of arm 'is engages one end ci a flap* per I 8 pivotaily connected at 'i9 to a post dii of a proportioning device di similar in construction to that described in connection with the pressure controller Eil. The iiapper T8 cooperates with a nozzle 82 which receives a regulated pressure supply of o erating fluid through pipes 23 and 84 from a source not shown, the latter pipe hav ing the usual restriction 85 so that the pressure in the nozzle is governed by the relative position A pipe iid, in

to communicate the nozzle with the diaphragm chamber 87 of the motor valve 65 which is oi the reverse acting type and is of similar construction to the motor valve 2l mounted in the steam conduit I3 supplying the main dryingroll section 9. A second pipe 83 connects the nozzle with the bellows 8S of the proportioning device Si which provides a proporticning action as gow erned by the rate of a spring sil in the same marrner as the proportioning device 25 referred to above. In operation, an increase in flow througl'i the orifice lo creates a proportional increase in differential pressure across the orifice. As this cours the float 'l2 moves down with the level of supporting mercury, rotates the lever i4 counterclockwise and moves the apper lil arr/ay from the nozzle 82 to decrease the nozzle pressure. Thereupon the prcportioning bellows 89 contracts and returns the dapper to a throttling relation at a reduced nozzle pressure. The motor valve 65 throttles the steam ow to the roll 5G to maintain the pressure drop across the oriiice and therefore the rate of ilow at a substantially oonstant value as determined by the control setting. The control setting is determined by the initial position of the ilapper 'I8 in respect to the nozzle t2 and as herein illustrated the setting may be varied by locking the operating arm 'it at desired angle to the loat operated lever ill.

It is important that a constant rate of flow be accurately maintained since changes in flow introduce errors in the response f the master controller to be described and there is therefore preferably provided means for maintaining a constant pressure upstream of the orifice '50, thereby restricting any tendency of the pressure to change to that portion of the conduit Gl which is downstream of the said oriiice. For this purpose a reducing regulator 90 of any usual construction may be employed. The regulator shown is of the direct acting type and is generally similar in construction to the valves and 65. It is mounted in the conduit Eil upstream of the orce 10 and has a diaphragm chamber 9| which is connected with the conduit on the downstream side of the valve by means of a pipe 92. The pressure in the diaphragm chamber 9| is opposed by a spring 93 which may be tensioned to provide a selected reduced pressure on the upstream side of the orice 1D, and since an increase of pressure tends to close the valve and a decrease in pressure tends to open it, the valve functions to maintain a substantially constant pressure upstream of the orifice.

As shown in Fig. l, the indicating roll 6B is in contact with the paper sheet I6 as it leaves the main drying roll section S, and since the roll is provided with a constant steam input, preferably but not necessarily, at a relatively low pressure, for example 6 p. s. i., changes in sheet moisture affect the rate of steam condensation in the roll and have a relatively large proportional effect on roll temperature. And the control apparatus shown in Fig. 1 responds to these relatively wide changes in roll temperature by responding to correspondingly relatively wide changes in roll pressure, although as shown in Figs. 2 and 3, response may be made to internal roll temperature or to the surface temperature of the roll.

Referring again to Fig. 1, a master controller, generally indicated at 95, which also may be of any well-known construction, is employed to respond to roll pressure changes and to provide an output pressure proportional thereto. The master controller includes a spiral coil 96, having a flapper actuating arm 91, and a manual control reset mechanism generally indicated at .'28 both of which may be similar to the coil 22 and manual reset 54-21 described in. connection with the pressure controller 20. The master controller also has a proportioning device of similaiconstruction to the proportioning device 25, shown in connection with the controller 20, together with a dapper |0| which is positioned by the coil arm 97 and proportioning device |00 in respect to a nozzle |02. Since the nozzle |02 is herein shown as being mounted above the flapper |0|, the bellows |03 and spring |64 are in the reverse position from that shown in the controller proportioning device 25. A sensitive adjustment |05 likewise similar to that in the controller 20, is also provided. The xed end of the coil 96 communicates with the steam conduit El by means of a pipe at a point between the valve 66 and the roll 60, preferably adjacent the roll in order that it may accurately reiiect changes in roll pressure. The controller nozzle |02 is connected with a regulated pressure supply of iiuid trom a source not shown through a pipe |06 having a restriction |07 of less capacity than that of the nozzle, pipe |06 being connected with a pipe |051 which communicates with the nozzle. A connection |08 between the pipe |061 and proportioning bellows |03 serves to communicate the nozzle pressure to the interior of the bellows |03 in the usual manner. It will be understood that a decrease of pressure in the roll 60 and therefore in the coil 96 causes the coil to wind up, thereby turning the arm 91 counterclockwise and moving the dapper |0| towards the nozzle |02 to increase the nozzle pressure. The resulting expansion of the bellows |03 moves the flapper away from the nozzle and returns the parts to a throttling relation to provide an increase in the nozzle pressure in the pipe |061, or in other words an increase in the master controller output pressure, on a basis which is proportional to the decrease in roll pressure. And since a relatively wide proportional change in roll pressure results from a relatively small change in sheet moisture, the master controller is sensitive to slight moisture changes and provides relatively large proportional changes in the output pressure, which changes may be utilized to govern the pressure in the rolls 0, preferably by resetting the control point of the pressure control instrument 20.

The control point resetting device 2G has a bellows ||0 having a xed mount through which the interior of the bellows is connected with the master controller output pressure pipe |061 by means of a pipe H2. The post 41 on which the lever 45 is pivotally mounted as hereinabove described, is secured to the free end ||3 of the bellows and to a disc ||4 between which and a fixed member ||5 an expansion spring ||6 is confined. Since the vertical position of the pivot 461 determines the control setting of the controller 20 in respect to the setting established by the rotary position of the coil arm 30 as provided by the manuallyoperated gear 54, the bellows |!0 functions to vary the control above and below the value established by the manual set mechanism on a basis which is inversely proportional to changes in roll pressure. Thus when the sheet moisture increases, a relatively wide drop in roll pressure occurs, thereby providing a relatively large proportional increase in the output pressure in the bellows l0. This increase in output pressure expands the bellows I0 proportionally thereto and correspondingly lowers the pivot 461 by an amount etermined by the rate selected for the spring H6. rlhus the lever 4G is rotated clockwise in accordance with the movement of the pivot 461, thereby positioning the flapper 24 nearer to the nozzle 23 and raising proportionally the pressure setting. And it will be understood that when a decrease insheet moisture occurs a `proportional decrease in master controller output pressure takes place and thereby the pressure setting of the controller is lowered proportionally to the decrease in moisture content.

In order to record changes in sheet moisture and in the pressure in the roll Sil, there is provided a recorder, diagrammatically shown at I I5, which may be of any usual construction and is preferably of the two-pen type. One pen, indicated at H61, is responsive to changes in indicating roll pressure as reflected in pipe 99 to which a Bourdon coil, not shown, by which the pen is operated, is connected by means of a pipe i I1. The other pen I I8 is operated by a Bourdon coil, also not shown, which connects with the cut-- put pressure pipe IIZ through a pipe lit. By means of a double range chart Iii, rotated in the usual manner by a clock not shown, and representing both pressure and sheet moisture deviation, the roll pressure is directly recorded by the pen H5, and changes in sheet moisture are indirectly recorded through changes in the master controller output pressure by pen IIB. which last mentioned changes are proportional to changes in the roll pressure and therefore to changes in sheet moisture content.

Fig. 2 illustrates an alternate construction wherein the transmitter coil 9S responds to the internal temperature of the roll Sil instead or to the roll pressure as shown in Fig. 1. The roll 60 to which the steam supply pipe 5I and condensate discharge pipe 62 are connected as shown in Fig. l, is provided with a temperature bulb 125 having the usual capillary tubing iZ which connects with the iixed end of the coil 96, `thereby providing a sealed thermal system which may be lled with a suitable expansible fluid. The bulb extends into the interior of the roll i and is sensitive to changes of temperature therein.

lThe operation of the master controller 95 is substantially identical to that described in Fig. 1, wherein the master controller responds to changes in the roll pressure. Since the temperature in the roll @il varies with the pressure when a change in sheet moisture occurs, lthe same relatively wide band of indication is provided. Thus the device functions in the same way as the pressure response shown in Fig. 1 since the coil 9S responds to changes in thermal system pressure which is substantially the .equivalent to changes in roll pressure.

In Fig. 3 there is shown a means for responding to changes in the surface temperature of that portion of the cylindrical surface of the roll 6e which is engaged by the sheet I6, the roll Eil being connected with the steam inlet conduit 6I and the discharge pipe V(i2 -as hereinabove described. For this purpose a surface temperature measuring device ISS of any well-known suitable construction is employed, preferably a measuring device of the type shown and described in the application for United States Letters l'atent of Andrew E. Bennett and Daniel S. Brown, filed February 16, 1951, lunder Ser. No. 211,336. The measuring device 13B may be mounted on a stand I3I at the cylindrical surface of the roll 6) and at a selected position on that porti-on of they surface which is engaged by the paper sheet. A capillary turbe i261 which corresponds to the tube I26 in Fig. 2 is connected to a bulb l2? in face temperature.

In thei operation of the device, the master ccntroller 't54 functions in the same way as already described. Since a constant steam input is supplied to the roll SG, a change in sheet moisture results in a relatively wide change not only in the internal temperature and pressure in the roll, but in the temperature of that portion of the roll surface which is engaged by the paper sheet, This will be evident when it is noted that the change in sheet moisture initially eiects a relatively wide change in the surface temperature of that portion of the roll engaged by the sheet since the quantity of steam supplie-d to the roll is not varied in a direction to counteract the moisture change. A nd it is equally clear that the relatively wide change in roll surface teniperature effects a substantially corresponding change in roll pressure and internal temperature. Thus as in the construction shown in Figs. l and 2, a relatively wide band of indication is provided, whereby the master controller is responsive to slight changes in sheet moisture and functions ixnmediately to reset proportionally the control setting of the instrument 26 to vary the heat input to the drying roll section 9 and maintain the sheet moisture content substantially at a selected value.

While the control mechanism hereinabove described functions to maintain the sheet moisture content to within extremely close limits, it has been found necessary when a break in the sheet It occurs and the sheet runs off of the machine, for the operator to manually reset the control mechanism to such lower pressure as is required t-o prevent overheating during the period when the paper sheet is not passing through the niachine and thereby overheating a considerable portion of the sheet when it is again introduced to the machine. HAnd the mechanism to be described functions with the control mechanism set forth above to change the control from a condition under which vthe `drying machine is operating under a sheet moisture load to a condition under which the vmachine is operating without the sheet moisture load, and thereafter to return the control setting to the value required to provide the proper moisture content when the sheet is again passed through the machine. YFor this purpose the solenoid valve I3?) is mounted in the output pressure line 5E from the controller .SE to the diaphragm chamber 8l of the Mcontrol valve v65. The valve 135 is of the three-way solenoid operated type and maybe of any Well-known construction. As herein illustrated it comprises a body having connections E36 and I3? which connect with pipe @t and a third connection 33 which connects with the output pressure line i951 of the controller by means of a `pipe Iss. Within the valve body a double seated valve member' ist cooperates with oppositely disposed ports itil and i612 and is connested by means of astem .hit to a core ld which together with a coil VAI constitutes a solenoid generally indicated at itt for actuating the valve member. The parts are arranged so that when the solenoid is deenergiaed by means to be described the port |42 isclosed and the port iili is open to connect the output pressure line fit with the diaphragm valve 5l of the valve SS. On the other han-d when the solenoid Iii-5 is energized the valve member It@ `closes the port ist and opens the port 142, whereby the output pressure line i361 Vfrom the controller 95 is connected lthrough the pipe i3d with that portion ci the pipe 'B5 which leads from the three-way valve to the diaphragm chamber 81 of the said valve 66. Means for energizing the solenoid is in the form of an electric gap switch as herein shown, generally indicated at |55, but it will be understood by those skilled in the art that any other well-known form or" device may be used for this purpose whether electrically, pneumatically or hydraulically operated.

The gap switch is provided with a mercury tube |5| which is secured by means of clips |52 (see particularly Fig. 4) to an operating 'member |53 having a support |54 pivoted at |55 on an upright |56 secured to a cover |51 with which a bellows casing |58 is provided. The tube |52' has the usual globule of mercury |59 and is soarranged that when tilted clockwise past its hcrizontal position as viewed in Fig. 4 the mercury globule will flow to the right to the position shown, and when tilted counterclockwise past its horizontal position, the mercury will flow to the left to the position shown in Fig. 1. A pair of conductors |66 having contacts |6| within the tube |5| together with the coil |45 surrounding the solenoid core |64 form part o a circuit whereby the solenoid may be energized from a. source or" electric current not shown when the contacts I6! are surrounded by the mercury |53.

Means for tilting the tube |5| is in the form of a bellows |62 disposed within the casing |56 and sealed to the cover |51 to provide a pressure chamber |63 externally of the bellows. Within bellows |62 is a compressi-on spring |64 which is confined between the cover |51 and the free end |65 of the bellows, The casing |58 is provided with a connection |66 into which a pipe |61 is threaded and communicates with the output pressure line |33 of the master controller 95. A rod |63, threaded at its outer end as indicated at |69, extends through an opening in the cover |51 and is attached at its inner end to a plate |10 which in turn is secured to the inner face of the free end |65 of the bellows. A pair of nuts |1| and |12 and lock nuts |13 are threaded on rod |68 and are suitably positioned and spaced so that the operating member |53, which extends into the spacing between the nuts, will be tilted clockwise by the nut |1| past its horizontal position at a selected low pressure in the chamber |63, and will be tilted counterclockwise by the nut |12 past its horizontal position at a selected high pressure in the said chamber, the pivotal connection being preferably provided With suicient friction, as by a friction washer |551, to hold the tube |5| at the tilted position to which it has been actuated by the nuts |1| and |12.

In operation, assuming that the output pressure from the controller 95 has an operating range from 3 p. s. i. to 15 p. s. i., the spring |64 being tensioned to provide a predetermined movement to the bellows |62 over this range of pressure change, and assuming further that a relatively high output pressure obtains so that the tube |5| is tilted to the position shown in Fig. 1, wherein the electric circuit is broken and the solenoid |46 is deenergized, the nut |1| may be positioned so that when the output pressure drops to 3 p. s. i. the nut |1| has moved down to a position to tilt the tube |5| clockwise past its horizontal position to the position shown in Fig. 4. When this occurs, the mercury |59 ows to the right, thereby completing the electric circuit. The nut |12 may also be positioned on the rod |68 so that when the pressure increases frcm 3 p. s. i. to a predetermined value,

.an increase in roll pressure takes place.

. 12 for example, 9 p. s. i., the nut |12 will be raised to a position to tilt the tube |5| counterclockwise past its horizontal position, whereup on the mercury will iiow to the left and break the electric circuit. Thus under the condition assumed, if the output pressure has been in excess of 9 p. s. i. the solenoid will deenergize un` til the pressure drops to 3 p. s. i. and thereafter the solenoid will remain energized until the output pressure has again risen to 9 p. s. i.

In describing the operation of the control mechanism shown in Fig. l, it may be assumed that the paper sheet I6 is passing through the machine, that the pressure controller 26 is set to maintain a steam pressure on the rolls l0 of 25 p. s. i., that the valve 65 is set to maintain a steam pressure of 20 p. s. i. upstream of the orice 16, and that the rate of ow controller 65 is set to maintain a constant steam input to the indicating roll 60 of 400 pounds per hour. Under these conditions and assuming that the output pressure range of the controllers is from 3 p. s. i. to 15 p. s. i. and that the steam pressure obtaining in the indicating roll 60 is approxihave its proporticning band adjusted, for example, to provide an output pressure of 15 p. s. i. when the indicating roll pressure is at 5 p. s. i and an output pressure of 3 p. s. i when the roll pressure is at '1 p. s. i. Thus when the roll pressure is at 6 p. s. i. the output pressure of the master controller will be at the midpoint of its range, namely 9 p. s. i., and the pneumatic set 26 in the pressure controller 20 will be at the midpoint in its range, namely, at the 25 p. s. i. pressure setting provided for the main drying section rolls by the manually operated gear 54. Again under these conditions the solenoid |46 of the valve |35 Will be deenergized and the rate of flow controller 65 will be governing the steam valve 66 to maintain a constant rate of flow through the orifice 10 of 400 pounds per hour. Also under these conditions changes in sheet moisture will be immediately reflected by changes in steam pressure in the roll 60, and the pneumatic set mechanism 26 of the pressure controller 20 will be varied by the master controllei` around the manual set point in proportional relation to changes in sheet moisture to vary the steam pressure in the main drying section and thereby to maintain the indicating roll pressure at substantially 6 p. s. i. I have found that under the usual operating conditions when the proportioning band of the master controller 95 is set to provide a change in output pressure from 3 p. s. i. to 15 p. s. i. on an indicating roll pressure change of plus or minus l p. s. i. from 6 p. s. i., a portion only of the output pressure operating range is required to maintain the indicating roll pressure well within the aforesaid pressure limits.

Let it be assumed that a break in the pacer sheet i5 occurs, that the sheet has left the rolls and that for this reason the major portion of the moisture load to which the machine has been subjected is suddenly removed. When this occurs, the rate of condensation in the indicating roll 6-2 is immediately reduced, and since a constant steam input of 400 pounds per hour is `being fed to the roll as governed by the controller 65, When the steam. pressure increases to '1 p. s. i., the output pressure in the master controller 95 decreases to 3 p. s. i., at which pressure the gap switch |50 completes the circuit through the conductors |60 to energize the solenoid of the valve ist?. The valve member ist is therefore raised to open the port |42 and close the port iti, whereby the output pressure from the controller 55 is cut on from the diaphragm chamber 3l of 4the steam valve and the output pressure from the master controller Q5 is connected thereto. Since the output pressure oi' the master controller S5 is at 3 p. s. i. at this time, ythe steam valve 55 will inimediately be actuated towards closed position and the stream pressure in the pipe below the orifice is will be immediately increased to the pressure of 20 p. s. i. maintained by the valve Thus the rate of iiow controller E55 will be rendered ineffective and the master controller S5 will continue to govern the valve S6 u'ntil its output pressure again reaches 9 p. s'. i. And since the' master controller 95 is set to maintain a pressure of 5 p. s. i. on the said roll and the steam flow now required to maintain this pressure is rolatively small, being just enough to take care or" the condensation caused by the heat transfer occasioned by a felt when employed and herein not shown, and. 'oy the atmosphere, the output pressure in the master controller will be just enough above the pressure of 3 p.- s'. i. for the purpose and will be well below the mid pressure of 9 p. s. i. Therefore the solenoid valve i355 will remain energized and the steam valve t6 will conn tinus to be governed by the master controller et.

In t e meantime the dropin output pressure of the master controller will also function to actuate the Ipneumatic set 26 of the pressure controller 2li to the low end of its pressure range. C=n the assumption that the range is adjusted to tbe on a 100% basis, the controller will immediately be reset at a point to close the steam valve 2i until the excess heat in the rolls has been removed oy condensation resulting from the transfer of heat occasioned by atmospheric conditions and, when a felt is employed, by the moisture content or the felt. After the excess heat has thus been removed, the continued transfer oi heat causes the pressure in the indicating roll to drop vbelow 7 s. i., thereby increasing the output pressure of the master controller S5 isufficiently to open the valves Sii 2i and provide the :proper amount of heat to meet the aforesaid conditions. Thereaiter the control will continue to function in lthis manner until the sheet is again :passed through the machine. When this occurs, as the' moist sheet passes over the indicating roll tt, the steam condenses more rapidly and the pressure starts to drop to the setting oi 5 p. s. i. The output pressure from the master controller 95 thereupon increases irom its former pressure, and when the pressure reaches. 9 p. s. i., the solenoid valve is again. deenergized. Thus the master controller is cut oi from. the chamber t? of the valve and the valve is again governed by the rate of flow controller By this means a constant steam input to the indicating roll of 400 pounds per hour is again :provided and the-pneumatic set mechanism 25 of the pressure controller again varies .the pressure settingon the main drying v It comprises the spiral coil 22, the proportioning' device 25, the nozzle and iapper 23e-2li, and the pneumatic reset mechanism 26'. The controller it functions together with the valve 2l to maintain a set pressure in the header i2 as' provided by the manual set mechanism 5th-2'! and by the reset mechanism 25 in a manner to be described.

Means for resetting the control point of the controller 20 in response to changes in the Yrate oi steam condensation in the indicating 'roll 6i! is in the forni of the rate of flow measuring instrument 65 wherein the parts are shown in the reverse position from that illustrated iii Fig". l. This includes the `rrierc'iiryV inahometei 6l' suit ably filled with mercury E8 supp rting the noa-t l2 `which is in operative connection with the flapper 'E3 by means of the lever l; The flapp'ei i3 is pivotally conn cte'd at' 'i9 to the proportioning device ii i and cooperates with the 'nozzle 32 which receives a regulated fluid pressure through the restriction 35 a pipe' 84 which in turn connects with the nozzle line 83 and with the pipe g8 cornVn municating with. the interior of tl-ie bellows' 8i? of the proportioning device 8l. The maiior'hetei" i is connected with the conduit 6l leading to the indicating roll et' by means of the pipes' se and il, but in this case the pipe 59 is connected with the conduit 6i down-stream of the orifice 'it and the pipe l! is connected with the conduit upstream oi' the said orifice.I Thus the action oi' the instrument t5 is reversed from that shown in l. An increase in oiif in the conduit Si provides a proportional increase in the pressure drop .across the orice lil, thereby raising the oat i2 and moving the happier 18 towards the nozzle El2 to provide a proportional increase in output pressure in the line 83. On the other hand, reduction in flow in the' conduit Si decreases the pressure drop across the oriiice' lil, thereby caus ing the float 'i2 to move down and raise the fla-p- Vper i6, whereby a proportional reduction in output pressure in the line 83 occurs'. The output pressure line 83 communicates with the interior oi the output pressure bellows H0 of the" pneu-V matic reset device 2S by means of a pipe 2e@ which includes the solenoid operated threeeway valve duit El is provided with the reducing valve Gtir which maintains a constant steam pressure ups'tream oi the orifice lil, and is also provided downstream of said orifice with the valve 56, to be governed in a manner to be described.

In operation, an increase in moisture in the sheet passing over the roll til causes a proportional increase in the rate of steam condensation in the said roll, thereby resulting in an increase in the rate of flow through the orifice iii. The increase in flow creates an increased prese sure drop across the orifice, thereby raising the iioat 'i2 and providing a proportional increase in output pressure in the line 33, in the pipe 2cd, and in the bellows llt` of the reset device 25. The bellows HQ thereupon expands and moves the dapper 2G towards the nozzle 23. And since the coil 22 turns the arm Si) clockwise to raise the apper 213 on an increase of pressure on the header i2, a higher pressure in the header is required to bring the iiapper into a throttling relation with the nozzle 23i Thus the pressure set ting of the' controller 2S is raised by an amount generally proportional to the increase in the rate of steam condensation in the roll 60 and therefore to the increase in sheet moisture. It will be understood that on a decrease shtmoisture 535 of similar construction to the valve heretofore described, and normally providing a. passage for duid through the pipe 256. The con-v the rate of steam condensation decreases proportionally thereto, and accordingly the reduced pressure differential across the orifice 'l0 results in a proportional decrease in output pressure of the controller 65 and in the reset bellows ||0 of the controller 20. Thus the bellows contracts and raises the flapper 24 from the nozzle 23 to provide a proportionally lower pressure setting for the controller 20. By this means changes in the rate of steam flow in the conduit 6| are utilized to measure changes in the rate of steam condensation in the roll E0 to vary the heat input to the main drying section 9 in a manner to govern the moisture content of the sheet passing through the machine. While this form of control is less sensitive than the preferred form of mechanism heretofore described, the means to be described function together with this type of moisture control to reduce automatically the machine temperature to a suitable value when a break in sheet material occurs, thereby preventing the material from becoming overdried or underdried when it is again passed through the machine.

For this purpose I provide the valve v66 in the conduit 6| downstream of the orifice l0 as in the preferred form of device shown in Fig. 1. However, instead of governing the valve 6B by the rate of flow instrument 65 as shown in Fig. 1, the valve is governed by the controller 95 which is of similar construction to that shown in Fig. l. As in Fig. 1, the coil 90 of the controller 95 is responsive to changes in pressure in the conduit downstream of the valve 68 by means of the pipe 99. And as therein described, an increase in pressure in the roll 60 causes the coil 95 to unwind and move the flapper |0| away from the nozzle |02. Since the nozzle |02 is supplied with iluid by the pipe |05 through the restriction |01, a proportional decrease in nozzle pressure results in the output pressure pipe |061. In the arrangement herein shown, the output pressure of the controller 95 in the pipe |051 is connected with the diaphragm chamber 81 of the reverse acting valve 66 by means of a pipe 20|. 'I'hus an increase in pressure in the roll 60 results in a proportional decrease in output pressure in the diaphragm chamber 8l, thereby causing the valve E6 to throttle the flow of steam to the roll 60. And when a decrease in pressure in the roll 60 takes place, the valve 66 functions to increase the flow of steam to the said roll. Thus the controller 95 governs the valve 66 to maintain the pressure in the indicating roll 60 substantially at a value established by the controller set mechanism 98. As in the preferred construction, I communicate the iiuid pressure in the output pressure line |061 with the connection |38 of the three-way valve |35. For this purpose a pipe 20|1 is employed which connects the pipe 20| with the valve. The three-way valve |35 is operated by the gap switch |59 but instead of responding to changes in output pressure in the pipe |061 as in Fig. 1, it responds to changes in output pressure in the rate of ow response instrument 65 with which it is connected by the pipe 83.

In describing the operation of the device, let it be assumed that the controller 29 is manually set to maintain a pressure of 25 p. s. i. in the main drying section 9, that the controller 95 is set to maintain a pressure of 6 p. s. i. in the indicating roll S0 and to provide an output pressure of 3 p. s. i. when the roll pressure is 7 p. s. i. and 15 p. s. i. when the roll pressure is 5 p. s. i., and that .the rate of now instrument 65 is arranged to provide an output pressure of 15 p. s. i. at a steam ilow of 425 pounds per hour, of 9 p. s. i. at a steam flow of 400 pounds per hour, and of 3 p. s. i. at asteam ow of 375 pounds per hour. Let it be assumed also that the range of the pneumatic set 26 of the controller 20 is adjusted to be on a 100 per cent basis. Under these conditions as long as the sheet is passing through the machine the controller will throttle the valve 66 to maintain substantially 6 p. s. i. in the roll 60, the quantity of steam required for the purpose varying proportionally with changes in the rate of steam condensation occasioned by changes in sheet moisture. For this purpose the output pressure ot controller 95 will vary around a mid-value, namely 9 p. s. i., and the rate of flow instrument 65 will respond to changes in flow across the orice 'l0 and vary the setting of the controller 20 around the manually set value of 25 p. s. i. in a manner to govern the moisture content of the sheet passing through the machine.

Under the conditions just referred to, when a break in sheet material occurs, the pressure in roll 60 will increase to 7 p. s. i., thereby reducing the output pressure of controller 95 to 3 p. s. i. and closing the valve 66. Thus the ow through the orice 10 will fall below 375 pounds per hour, the output pressure of the rate of ow instrument 65 will drop to 3 p. s. i. and on the assumption that the gap switch |50 energizes the solenoid |44 of the three-way valve |35 at this pressure, the reset bellows ||0 will be disconnected from the instrument 65 and will be connected with the pipe 20|1 which communi- Cates with the output pressure line |061 of the controller 95. Since the output pressure of the controller 95 is now at 3 p. s. i., the valve 66 wi1l be closed and the pneumatic set mechanism 25 will function to close the main steam valve 2|. Thereafter the controller 95 will continue to operate the valve 66 to permit such steam as may be required to maintain the pressure in roll 60 substantially at 6 p. s. i. through the period when the machine is without a sheet moisture load. The controller 95 will also throttle the valve 2| to permit such steam to enter the main drying section as may be required to maintain the said section at a temperature suited to the sheet when again passed through the machine. And since the quantity of steam required for the purpose is relatively small, the output pressure of the instrument 65 will be well below that required by the gap switch |50 to deenergize the solenoid of the three-way valve |35 on the assumption that a suitable pressure such as 9 p. s. i. is required for this purpose.

Let it be assumed that the sheet is again introduced to the machine and that the usual moisture load is then encountered. The rate of condensation in the roll 60 will thereupon immediately increase and when the output pressure of instrument 65 reaches 9 p. s. i., the gap switch |50 will deenergize the solenoid of the three-way valve, thereby disconnecting the controller 95 from the pneumatic set mechanism 26 of the controller 20 and again connecting the rate of ow instrument 55 thereto. Thus the controller 95 will continue to maintain a pressure of substantially 6 p. s. i. in the roll 60 and the instrument 65 will again vary the setting of the controller 20 around the manual set point of 25 p. s. i. It will be understood that while the controller 95 is shown as being responsive to pressure in the roll 60, it may also be arranged to respond to roll temperature in the manner described in connection with Figs. Zand 3.

Vmoisture indicating section, rst means for varying the supply of heat to the main drying section, a conduit having a source of steam supply and connected with the said indicatingsection, secondmeans responsive to changes in steam flow through said conduit, said changes being in proportional relation to changes in the rate oi steam condensation in the said indicating section, third means responsive to changes in the rate of steam condensation in the said indicating section, rone of said second and third means being inoperative connection with the rst means for Vvarying the supply of heat to the main section iii-proportional relation to said changes in the rate of steam condensation, and mechanism responsive proportionally to said changes in the Vrate of steam condensation and activated when the rate of steam condensation drops below a predetermined value to transfer the control from one of said second and third means to the other said second and third means to reduce the heat '@lue o fnthe main drying section to said selected value.

2..In a control mechanism for governing the heat input to a sheet material drying machine tomaintain themoisture content of sheet material passing therethrough at a selected value vand to reduce the heat input to a selected value during a vperiod when the material is off the machine, said machine including a main drying section having a source of heat supplyV and a sheet moisture indicating section, first means for varying the supply of heat to the main drying section, a conduit having a source of steam supply vand connected with the indicating section, a

. restriction in said conduit, second means responi sive to changes in steam flow through said restriction, said changes being in proportional relation to changes in the rate of lsteam conl-densation rin the indicating section, a valve in .theconzluit downstream of said restriction, third l `meansresponsive to changes in the' rate of steam condensation in the indicating section, one of said second and third means 'being in .operative i yconnection With'the first means for varying the supply of heat to the main section in proportional second and third means to the other of said second and third means to reduce the heat value of the main dryingsection to said selected value.

3. In-a control mechanism for governing the heat input toa sheet material-drying machine -to maintain the moisture content of sheet material Ypassing therethrough at a selected value and to reduce the heatkinput tof'a selected Value during la period When the material'is off the machine,

said machine including a main drying section having a source of heat supply and a sheet moisture indicating section, rst means for varying the supply of heat to the main drying section,'a conduit having a source of steam supply and connected with the indicating section, a restriction in said conduit, second means responsive to changes in steam iiow through said restriction,

said changes being in proportional relation to changes in the rate of steam condensation inthe indicating section, a valve in the conduit downstream of said restriction and a valve in the conduit upstream of said restriction, third means .responsive to changes in the rate of steam condensation in the indicating section, one yof's'aid second and third means being in operative'conneoticn with the first means for varyingfthe'supply of heat to the main section in proportional relation to the said changes in' the rate of steam condensation, and at least one of said second and Vthird means being in operative connection with one of said valves, and mechanism responsive proportionally to said changes in the rate of steam 4condensation and "activated when the rate :of

steam condensation drops below a predetermined value to transfer the control from one of said second and third means to theother ofsaidsecond vand third means to reduce the heatv value of the rnain drying section to said selected value,

4. In a control mechanism for governing the heat input to a sheet material drying machine to maintain the moisture content ofsheetmaterial passing therethrough ata'select'e'd value, said machineincluding a main drying sectionan'd a sheet moisture indicating sectionyand each of said sections being in heat transfer relation with the said sheet material, rst means for varying heat from a source of supply to the main section, second means maintaining a constant rate of heat input from a source of supply tothesheet moisture indicating section, third means responsive to a change in the rate of heat transfer in said sheet moisture indicating section andin'operative connecti-n'with said first meansto vary the supply of'heat to the main section in'proportional relation to 'the said change in the rate of heat transfer, 'and mechanism in operative connection with said second-and third means responsive proportionally to said changes in the rate of vheat 'transfer and activated whenthesaid rate of heat transfer drops below `a predetermined vvalue to limit the control to said third means for varying the heat input during fa period when the vsaidrate of heat transfer remains below'a predetermined value.

sive to changes in the rate of heat transfer in thesheet moisture-indicating-sectionto vary the heat Tvalue maintained ein Asaid main section 4'in proportional relation to said changes inthefrate `of -heat transfer, and mechanism responsivef'proportionally to changes inthe said rate offhefat transfer an`d`in operative association with said second and third means to transfer the control to said third means to govern the rate of heat input to the sheet moisture indicating section when the said rate of heat transfer falls below a predetermined value.

6. In a control mechanism for governing the heat input to a sheet material drying machine to maintain the moisture content of sheet material passing therethrough at a selected value, said machine including a main drying section and a sheet moisture indicating section, and each of said sections being in heat transfer relation with the said sheet material, first means governing the supply7 of heat to the main section to maintain a selected heat value therein, second means maintaining a constant rate of heat input to the sheet moisture indicating section. control point setting means associated with said first means, third means responsive to changes in the rate of heat transfer in said moisture indicating section and in operative connection with said control point setting means for varying the heat value maintained in said main section in proportional relation to said changes in the rate of heat transfer, and mechanism responsive proportionally to changes in the said rate of heat transfer and in operative association with said second and third means to transfer the control to said third means to govern the rate of heat input to the sheet moisture indicating section when the said rate of heat transfer falls below a predetermined value.

7. In a control mechanism for governing the heat input to a sheet material drying machine to maintain the moisture content of sheet material passing therethrough at a selected value, said machine including a main drying section and a sheet moisture indicating section, and each of said sections being in heat transfer relation with the said sheet material, a first conduit having a source of steam under pressure providing a supply of steam to the main section, a second conduit having a source of steam under pressure providing a supply of steam to the sheet moisture indicating section, a rst valve in said first conduit for varying the supply of steam to the main section, a first controller having a source of power and responsive to changes in heat value in the main section in operative connection with said first valve to maintain a selected heat value in the said main section, a second valve and a restriction in said second conduit, a second controller having a source of power and responsive to changes in flow through said restriction in operative connection with said second valve for maintaining a substantially constant rate of steam flow to said sheet moisture indicating section, a. third controller having a source of power and responsive to changes in the rate of steam condensation in the sheet moisture indicating section in operative connection with the said first controller for varying the heat value setting of said first controller in proportional relation to the sa-id changes in the rate of steam condensation, and mechanism responsive proportionally to said changes in the rate of steam condensation and activated when the rate of steam condensation drops below a predetermined value to operatively connect said third controller with said second valve to govern the steam input to said sheet moisture indicating section until the said rate of heat transfer exceeds a predetermined value.

8. In a control mechanism for governing the heat input to a sheet material drying machine to maintain the moisture content of sheet material passing therethrough at a selected value, said machine including a main drying section and a sheet moisture indicating section, and each of said sections being in heat transfer relation with the said sheet material, a first conduit having a source of' steam under pressure providing a supply of heat to the main section, a second conduit having a source of steam under pressure providing a supply of steam to the sheet moisture indicating section, la first valve in said first conduit for varying the supply of steam to said main section, a iirst controller having a source of power and responsive to changes in heat value in the main section and in operative connection with said first valve to maintain a selected heat value in said main section, a restriction in said second conduit, a second valve downstream of said restriction, a third valve upstream of said restriction, a Second controller having a source of power and responsive to changes in flow through said restriction in operative connection with said second valve for maintaining a constant rate of steam flow to said sheet moisture indicating section, a third controller having a source of power and responsive to the rate of steam condensation in the sheet moisture indicating section and in operative connection with said first controller for varying the heat value setting of said first controller in proportional relation to the said changes in the rate of steam condensation, and mechanism responsive proportionally to changes in the said rate oi steam condensation and operatively connecting said third controller with one of said second and third valves when said rate of condensation drops below a predetermined value to govern the rate of steam input to said sheet moisture indicating section.

9. In a pneumatic control mechanism for governing the heat input to a sheet material drying machine to maintain the moisture content of sheet material passing therethrough at a selected value, said machine including a main drying section 'and a sheet moisture indicating section, and each of said sections being in heat transfer relation with the sheet material, a iirst conduit having a source of steam under pressure connected to the main section, a second conduit having a source of steam under pressure connected to the sheet moisture indicating section, a iirst fluid pressure operated valve means in said iirst conduit, a irst controller responsive to changes in heat value in the main section and varying pressure to said valve means from a. source of fluid pressure in proportional relation to said changes in heat value, a pneumatic control point setting mechanism associated with said first controller having an element responsive to changes in uid pressure for varying the setting of said controller, a. second uid pressure operated valve means for varying steam flow through said second conduit, a second controller having a source of fluid pressure and responsive to changes in the rate of flow through said second conduit to provide variations in output pressure in proportional relation thereto, a first fiuid line connecting the output pressure from said second controller with said second valve means to maintain the rate of steam input to the said sheet moisture indicating sec tion at a substantially constant value, a third controller having a source of fluid pressure and responsive to changes in the rate of steam condensation in the moisture indicating section to provide variations in output pressure in proportional relation thereto, a fluid connection from the output pressure of said third controller to the element of said control point setting mechanism "for varyingthe controller setting in proportional relation to said changes in the rateof steam condensation, a second fluid line connecting-the output pressure of said third controller with lsaid) second valve means, a third-valve-means governring fluidflow'through each of sai-d'uid-lines, and 'mechanism responsive proportionally to changes Vin ,the said rate of steam condensation and in operative connection With saidl third valve means to open said iirstiiuid line and close said second fluid line when the` rate of steam condensation exceeds a predetermined value and to open said. second iluid line and close said nrst fluid line when the rate ofcondensation drops belowa pre-- determined value. I

Ina control mechanism for governing-the heat input to a sheet material drying machine to maintain the moisture content of sheet material passingv therethrough at aselected value, said machine includ-ing a vmain drying section and'a sheetmoisture indicating section, and each of said sections being heat transfer'relation with `the said sheet material, first means for varying heat from a .source of supply to the main section, a source of 'heat supply connected with lthel sheet moisture indicating section, second means responsive to changes-in. the rate of heat input to the `sheet moisture indicating section and in operative connection with said rst means to vary the heat supplied to the main section in lproportional relation to Vthey said changes in the rate of heat input'. third Imeans responsive to changes 'in the rate lof heat transfer in the moisture indicating section and varying the rate of heat input to said section in proportional relation to the said changes in the rate of heat transfer, and mechanism in operative connection with said second and third means responsive proportionally to the rate of heat transfer' and activated when the said rate of heat transfer drops below a predetermined value to limit the control to said third means for varying the heat input during a period when the said rate of heat transfer remains below a predetermined value.

11. In a control mechanism for governing the heat input to a sheet material drying machine to maintain the moisture content of sheet material passing therethrough at a selected value, said machine including a main drying section and a sheet moisture indicating section, and each of said sections being in heat transfer relation with the said sheet material, a first conduit having a source of steam under pressure providing a supply of heat to the main section, a second conduit having a source of steam under pressure providing a supply of steam to the sheet moisture indicating section, a first valve in said nrst conduit for varying the supply of steam to the main section, a first controller having a source of power and responsive to changes in heat value in the main section in operative connection With said first valve to maintain a selected heat value in said main section, a restriction in said second conduit, a second valve downstream of said restriction, a third valve upstream of said restriction, a second controller having a source of power and responsive to changes in ilow through said restriction, a third controller having a source of power and responsive to the rate of steam condensation in the sheet moisture indicating section and in operative connection with one of said second and third valves to vary the rate of steam flow to the indicating section in proportional relation to the said changes in the rate of steam condensation, means operativefiy'connecting either one'or'the amener-me am second andl third controllers with the said rst controller to vary the heat value maintained 'in the main section, and mechanism governing said means responsive proportionally to said changes in the rate of steam condensation and activated rst controller.

12. In a pneumatic controlapparatus for: governing the-heat input to'a'sheet moisture drying lmachine including a main drying section and Aa -sheet moisture indicatingsection, rst-pneumat'- ically` oper-ated control 'means having a source of iluid pressure for governingl the-heat input lfrom a source of supply to themain drying-'sec- -tion, a conduitconnecting a'sour'ce of'steamsupplyto the moisture indicating section, :a restriction and apneumatically operated valve in said conduit, second pneumatically operated control means varyingfluid operating pressure from a source of supply in proportional relationvto changes in steam now through said restriction,

thi-rd pneumaticaliy operated control means varying fluid pressure from a source of supply-in proportional relation to changes in the rate of steam condensation inthe sheet moistnre'indicating section, a pneumatically operated control point settingdevice governing the control lsetting of the first control means, a first huid line connecting the control point setting device with the operating pressure from the said second control means, a second huid line connecting said device with the operating pressure from the said third control means, and a third fluid line connecting the operating pressure from the said third control means with said valve to maintain a substantially constant heat value in the sheet moisture indicating section, valve means normally closing the second fluid line, and mechanism in operative connection with the said valve means and responsive to changes in the said rate of steam condensation, said mechanism being activated when the said rate of steam condensation drops below a predetermined value to actuate said Valve means to open 1the second fluid line and close the rst uid 13. In a pneumatic control apparatus for governing the heat input to a sheet moisture drying machine including a main drying section and a sheet moisture indicating section, rst pneumatically operated control means having a source of fluid pressure for governing the heat input from a source of supply to the main drying section, a conduit connecting a source of steam supply to the moisture indicating section, a, restriction and a pneumatically operated valve in said conduit, second pneumatically operated control means varying fluid operating pressure from a source of supply in proportional relation to changes in steam flow through said restriction, third pneumatically operated control means varying fluid pressure from a source of supply in proportional relation to changes in the rate of steam condensation in the sheet moisture indicating section, a pneumatically operated control point setting device governing the control setting of the rst control means, a iirst fluid line connecting the control point setting device with the operating pressure from the said second con- 23 trol means, a'second fluid line connecting said device with the operating pressure from the said third control means, and a third fluid line connecting the operating pressure from the said third control means with said valve to maintain a. substantially constant heat value in the sheet moisture indicating section, valve means normally closing the second fluid line, and mechanism in operative connection with the said valve means and responsive to changes in the said rate of steam condensation, said mechanism being activated when the said rate of steam condensation drops below a predetermined value to actuatc said valve means to open the second fluid line and close the first fluid line, and said mechanism being again activated when the said rate of condensation increases to a, predetermined value to actuate said valve means to open the first fluid line and close the second fluid line.

14. In a control mechanism for governing the heat input to a sheet material drying machine including a. main drying section and a sheet moisture indicating section, a first controller having a source of power and governing means for varying heat input from a source of supply to the main section to maintain the heat in said section at a constant selected value, a second controller having a source of power and responsive to changes in the rate of flow of steam from a source of supply to the sheet moisture indicat- 30 .ing section, a third controller having a source Aof power and responsive to changes in the rate of steam condensation in the said moisture in- 24 dicating section, a power operated device for varying the rate of steam flow to the moisture indicating section, a power operated device for varying the control setting of the said first controller, first power transmission means adapted for the connection of one of said devices with said second controller, second power transmission means adapted for the connection of said one of said devices with said third controller, third power transmission means connecting the other of said devices with said third controller, and power operated mechanism for connecting said rst means and disconnecting said second means and for connecting said second means and disconnecting said first means, said mechanism being responsive to changes in the said rate of steam condensation and being activated when the said rate exceeds a predetermined value to connect said first means and disconnect said second means and when the said rate drops below a predetermined value to connect said second means and disconnect said rst means.

ANDREW E. BENNETT.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,142,037 Stamm Dec. 27, 1938 2,208,784 Armstrong July 23, 1940 2,401,832 Krogh June 11, 1946 

